1. Field of the Invention:
The present invention relates to a photosensitive material drying device for drying a photosensitive material with radiant heat, which is suitable for use in, for example, an automatic developing machine.
2. Description of the Related Art:
In an automatic developing machine, photosensitive material such as photographic film (hereinafter called "film"), photographic paper, etc. are subjected to developing, fixing and washing processes while being conveyed by rollers, followed by transfer to a drying unit, where a drying process is carried out.
As an example, an automatic film developing machine is discussed below. In general, the drying unit is provided with a drying device, which has a plurality of far infrared radiation heaters disposed therein along the direction orthogonal to a film conveying direction, i.e., along the transverse direction of the film, and a plurality of reflectors disposed behind the far infrared radiation heaters in confronting relationship with the film.
When the wavelength of far infrared radiation generated from each of the far infrared radiation heaters is about 4 to 5 .mu.m for each surface temperature of each of the far infrared radiation heaters as shown in FIG. 6, the amount of heat radiated from each of the far infrared radiation heaters increases. In addition, a difference develops between the transmissivity of far infrared radiation through a film at the time that the density D is about 0.6 (i.e., D.apprxeq.0.6)(halftone) and the transmissivity of far infrared radiation through the film at the time that the density D is about 0.1 to 0.2 (i.e., D.apprxeq.0.1 to 0.2)(non-exposed original image) as illustrated in FIG. 7.
Thus, even if the amount of heat applied to the film is kept constant, the amount of heat to be actually absorbed by film changes depending on the density of the film. Thus, as the density of the film becomes higher, the amount of heat absorbed by the film increases.
In a radiant-heat drying process using such far infrared radiation heaters, when the density of the film is high, the film is changed in a short time from a constant-drying-rate condition where the drying speed of the film is fast, water or moisture adhered to the surface of the film is used as latent heat vaporization and the surface temperature of the film is kept constant, to a falling-drying-rate condition where the surface temperature of the film is raised due to a reduction in the moisture on the surface of the film. When the radiant-heat drying process continues in the falling-drying-rate condition as it is, the surface temperature of the film increases excessively. As a result, the film tends to become very glossy and lacks uniformity. Further, the film is liable to curl and melt. While the amount of heat radiated from the far infrared radiation heaters can be adjusted in advance when the density of the film is high, the film drying process cannot be sufficiently carried out when the density of the film is low.
Therefore, a photosensitive material drying device of a type wherein hot-air suppliers are provided together with far infrared radiation heaters to determine, based on the percentage of moisture content and the like of a film, whether the film is in a constant-drying-rate condition or a falling-drying-rate condition has been disclosed in Japanese Patent Application Laid-Open No. 3-54560. With this device, when the film is changed from the constant-drying-rate condition to the falling-drying-rate condition, radiant-heat drying by the far infrared radiation heaters is changed over to hot-air drying performed by the hot-air suppliers to thereby dry the film by controlling an increase in the temperature of the film being dried by hot-air drying.
However, in the above-described conventional photosensitive material drying device, it is necessary to provide both the far infrared radiation heaters and the hot-air suppliers and to change over radiant-heat drying to hot-air drying. Thus, the mechanism of the photosensitive material drying device is complicated.